Display devices such as television receivers and computer visual display units normally have manually operated brightness and contrast controls. These controls allow the user to adjust the brightness and contrast of the displayed picture by a desired amount. Conventionally, each control has been implemented by a variable resistance potentiometer comprising a track of electrically resistive material. Each end of the track is connected to a separate electrical terminal. A third terminal or "wiper" is held in contact with the track by a spring bias. The wiper can be moved along the length of the track to vary the resistance between the wiper and one of the other two terminals. In a rotary action variable resistance potentiometer, the wiper is fixed to a rotatable spindle and held in contact with an annular track. A linear potentiometer has the wiper fixed to slideable support and held in contact with a linear track.
Variable resistance devices such as rotary action and linear potentiometers have a disadvantage in that friction between the wiper and the track causes wear and eventually failure of the device. Furthermore, some potentiometers are too large to be accommodated within desired equipment enclosures.
There is presently available a type of domestic television receiver (TVs) responsive to signals transmitted from a remote control device. The remote control device allows an operator to make a TV channel selection from a viewing position remote from the TV. In addition the remote control device enables the operator to select a desired TV picture brightness. The remote control device implements a selection by transmitting a digitally coded instruction to the TV set in the form of a beam of pulse modulated infra red radiation. Generally, the instruction consists of either a) a "start" signal instructing the TV set to start increasing or decreasing the TV picture brightness, or b) a "stop" signal instructing the TV set to stop increasing or decreasing the TV picture brightness, depending on the selection made by the operator. The operator is thus provided with the convenience of adjusting the brightness and contrast of the TV picture without moving from a viewing position distant from the TV. However, the remote control device operates under power supplied by a battery. The battery must therefore be regularly replaced or recharged to maintain the remote control device in an operational state. Furthermore, the remote control device comprises complex transmitter circuitry and the host TV comprises equally complex decoder circuitry. Although the cost of such complex circuitry can become acceptable where production quantities are high, in other applications the cost can be prohibitive.